Multiple stage, hydraulic jet propulsion apparatus for water craft



Oct. 15, 1968 G R. ASCHAUER 3,405,526

MULTIPLE STAGE, HYDRAULIC JET PROPULSION APPARATUS FOR WATER CRAFT Filed March 1, 1967 United States Patent ABSTRACT OF THE DISCLOSURE Hydraulic jet propulsion apparatus for waterborne craft having multiple stages of different type pumps operating at different speeds.

Cross reference Thepresent invention is in the nature of an improvement over my co-pending US. patent application Ser. No. 495,640 filed Oct. 13, 1965, which is now Patent No. 3,328,961, and entitled, Multiple Stage Hydraulic Jet Propulsion Apparatus for Water Craft.

Background 0 the invention In order to have adequate pressure rise through the propulsion unit and resulting high jet velocities for high speed boats, the velocity of the water mass flow through the unit must be raised in stages. 7 7

Prior art propulsion units have used multiple-stages of pumps but these pumps have usually been of the same size and/or speed as one another. The US. patent to Hamilton, No. 3,083,529, issued Apr. 2, 1963, is an example of this type.

In other prior art devices, pumps of different sizes or types were used at the same speed or at different directions of rotation, for example, the US. Patent 3,269,111, issued on Aug. 30, 1966, to E. F. Brill.

In many instances, as only a low pressure rise can be obtained across the first stage because only atmospheric pressure is available to push the water in at the intake when the boat is stationary, the subsequent stages are also only low pressure rise stages because they all have the same water flow, in gallons per minute (GPM), and speed of the impeller in revolutions per minute (RPM).

As to the efiiciency of centrifugal pumps in general, efficiency depends on specific speed (hydraulic design), capacity (size of pump), inlet condition (inlet head), internal running clearances, surface roughness (casing and impeller material), and stufiing box friction. The influences of specific speed and capacity are dominating in most cases.

In the design of marine jets of the type to which the present invention relates, the maximum propulsive efficiency depends among other things, on the unit size and weight, GPM of water flow, boat stall thrust and accelerating capability and allowable specific speed. High efiiciency requires large flow of water and low jet velocity consequently low jet pressure. Specific speed is represented by the known formula where RPM is the speed of the impeller, GPM is the water flowing through and H is pressure head in feet of water generated by the pump. From the above formula, it is seen that low specific speeds require high head combined with relatively low capacity and speeds of rotation.

In marine jets it is desirable to have the highest practical water mass flow but this flow is limited due to the physical strength and size of the water-borne craft. In order to have a specific speed (Ns) which is of a reasonably low value in the first stage, the present invention utilizes a large diameter, low speed, first stage impeller. As the atmospheric pressure is the only force pushing the water into the intake opening when the craft is stationary, the present impeller design provides a large intake area and consequently good initial force due to atmospheric pressure, to thereby push water into the intake. This permits use of a lower specific speed (Ns) value, which is desirable at this stage because the RPM can be less.

Summary of the invention The invention provides a particularly efiicient, multiplestage, hydraulic jet propulsion apparatus for waterborne craft in which the pumps of the diiferent stages are of different types and operate at different speeds.

The present invention provides a multi-stage apparatus of the above type in which the first stage pump is of the axial flow type and acts as a supercharger pump; the second stage pump is of the mixed flow type and which constitutes the main pump for the apparatus and develops the great majority of the horsepower; in addition, this second stage pump is driven at a higher speed than the first stage pump. It is thus possible to utilize a slower speed, lower horsepower first stage pump for the supercharging or packing of the water into the main second stage pump which in turn utilizes a higher allowable specific speed, resulting in a particularly efiicient marine jet. This combination of an axial flow pump feeding, that is, supercharging, a subsequent mixed-flow type of pump, with the latter mixed flow pump turning at a considerably higher speed, provides a particularly efficient unit capable of using the slower speed and lower horsepower pump to initially pack the second stage, main pump of higher specific speed. The arrangement is such that the mean diameter of the mixed flow pump is greater than the mean diameter of the first, axial flow pump, and this permits a slower speed for the mixed flow pump than would be possible using an axial flow pump as the second stage. With the present arrangement, a greater pressure rise is possible through the second stage, mixed flow type pump. Furthermore, the general flow path of the water is one having few and gentle turning losses.

A more specific aspect of the present invention relates to apparatus of the above type which has a carefully shaped, diffusing type inlet duct which minimizes friction losses and in which the inlet velocity is considerably higher than the velocity of the inrushing water just ahead of the first pump. With the velocity of the water just ahead of the first pump reduced, the pressure is greater in this area, and it is this pressure increase ahead of the first pump which is effective in reducing cavitation.

These and other objects and advantages of the present invention will appear as this disclosure progresses, reference being had to the accompanying drawings in which:

Brief description of the drawing The drawing is a longitudinal, cross-sectional view through a portion of a watercraft embodying apparatus of the present invention, certain parts being shown in section or broken away for clarity of the drawings.

Description of preferred embodiment Referring in greater detail to the drawings, the propulsion unit' U with the housing H is mounted with the forward end of its intake portion 1 flush with the bottom 2 of the watercraft C, and rearward, restricted end 3 of the housing extends through the stern of the craft in accordance with conventional practice. An intake grill 1g may be provided below the hull of the craft, if desired. The forward intake portion 1 of the housing is of the diffusing type in which the water is diffused as it approaches the first pump, thereby decreasing its velocity and increasing its pressure. This is due to the fact that 3 the cross sectional area of the inlet side 1a of the intake portion is less than the dischargeside 1b adjacent the first pump, to be described. 7

A nozzle N extends rearwardly beyond the stern for receiving the stream of water from the housing in the boat and discharging it to propel, steer or reverse the boat in the known manner. The nozzle may be of the type shown in my Patent No. 3,251,185 which issued May 17, 1966, and is entitled, Jet Propelled llVater Craft, or it may be of a modified, narrower form of the nozzle shown in my Patent No. 3,183,878, which issued May 18, 1965, entitled, Hydrojet Propulsion Unit for Water Craft.

A power plant in the form of an internal combustion engine 5, for example, drives a lay shaft 5a which in turn drives a shaft 6 through a gear reduction unit 7. More specifically, the reduction unit through its gears 7a and 7b, drives the shaft 6, and through its gears 70 and 7d, drives the sleeve 8 which is fixed by a key 8a to the gears 7d.

A first stage pump 10 is of the axial flow type and is fixed to the sleeve 8 and is driven thereby to form a relatively low speed pump which acts to supercharge or pack the water into a second stage pump 12. This first stage axial flow pump forces the water in a generally axial direction with a minimum of water straightening being required, and directly to the second stage pump, and produces good water acceleration. The mean diameter of pump 10 is indicated by the dotted line 11, the point of discharge being at the rear of the blade, as at 11a.

The second stage pump 12 is fixed to and driven by the shaft 6 to form the main, high-speed pump of the apparatus. Its mean diameter is indicated by the broken line 13.

The second stage pump 12 is of the mixed flow type and operates at a higher speed than the first stage. The main i pump, that is, the mixed flow, second stage pump delivers the great majority of the horsepower, for example, in a jet developing 258 horsepower, it would develop approximately 192 horsepower while the first stage, axial type pump would develop the remaining 66 horsepower.

The mixed fiow impeller or pump discharges at an angle to the shaft axis that is less than 90 degrees and its greater than zero degrees. That portion of the housing which extends from the intake side of the first stage pump to the intake side of the second stage pump is generally of straight or cylindrical shape. The housing then diverges rearwardly from the inlet side of the second stage pump to the discharge side of the second stage pump. Then the housing converges severely at its discharge portion.

The outer ends of the pump blades are of the free or unsupported type and closely follow the contour of the housing which complements and surrounds them. Wear rings 13 may be provided in the housing adjacent the blade tips.

Fixed straightening vanes are provided behind each pump for straightening out or relieving the spin of the water as it leaves the pump. For example, vanes 14 are secured within the housing and are located behind the first stage pump 10. These vanes are fastened together at their radially inner ends by the hub 14a which also forms a support for the bearings 14b and 14c which rotationally support, respectively, the sleeve 8 and the drive shaft 6.

An inspection cover 14d is provided for access to the apparatus for inspection and maintenance, and this cover may contain one or more vanes 14 as required. The housing includes a seal 15 between the sleeve 8 and the housing fairing 16 located just ahead of the hub of pump 10.

It will be noted that the mixed flow pump 12 diverges toward its rear end and delivers water to the rear discharge portion 19 of the housing. This discharge portion is of rearwardly diverging shape at its forward end 19a and then is of rearwardly converging shape at its rearward end 19b where it is in communication with the nozzle N. The discharge portion 19 of the housing also has a series of straightening vanes 20 which act to rec eive the water from the second pump and reduce the circular movement or spin of the water.

.Rsum

With the present invention, a particularly efticient twostage, two-speed hydraulic jet propulsion unit has been provided which uses a relatively slow speed, low horsepower, axial flow type pump to initially [pack or supercharge water into the second stage pump of the mixed flow type. This combination of multistaging does not cause either pump to lose its efficiency and with the mixed flow pump operating faster than the first stage pump, a particularly efficient unit is the result.

The smaller mean diameter of the first stage, axial flow type pump, as compared to the second stage, mixed flow type pump, results in a lower permissible speed for the mixed flow pump (even though it is faster than the first stage pump) than would be possible with an axial flow type pump used as the second stage pump. A greater pressure rise through the second stage pump of the present invention results and few and small turning losses are present.

Various modes of carrying out the invention are contemplated as being within the scope of the following claims particularly pointing out and distinctly claiming the subject matter which isregarded as the invention.

I claim:

1. A multi-stage, hydraulic jet propulsion unit for waterborne craft comprising, a housing having a forward intake portion and a rearward discharge portion for discharging rearwardly of the stern of the craft; a first stage, axial flow pump in said housing; a second stage, mixed flow pump in said housing and located rearwardly of said first stage pump for receiving water therefrom; straightening vanes located rearwardly of each of said first and second stage pumps; and means for rotationally driving said pumps and said second stage pump faster than said first stage pump.

2. A unit as defined in claim 1 further characterized in that said forward intake portion is of the diffusing type and has an inlet side and a discharge side, said inlet side being of smaller cross sectional area than said discharge side.

3. The unit as set forth in claim 1 further characterized in that said housing is of substantially cylindrical shape from the inlet side of said first stage pump to the inlet side of said second stage pump, and the said housing then diverges rearwardly from the inlet side of said second stage pump to the discharge side of said second stage pump, and then said housing converges rearwardly at its discharge portion.

4. The propulsion unit described in claim 1 further characterized in that said means for rotationally driving said pumps includes an engine and gear reduction unit, said pumps being in co-axial alignment and driven by a sleeve and a shaft, said sleeve and shaft each being connected to said gear reduction unit for being rotationally driven.

5. The propulsion unit described in claim 3 further characterized in that said means for rotationally driving said pumps includes an engine and gear reduction unit, said pumps being in co-axial alignment and driven by a sleeve and a shaft, said sleeve and shaft each being con- ,nected to said gear reduction unit for being rotationally driven.

6. A multi-stage, hydraulic jet propulsion unit for waterborne craft comprising, a water-conveying housing having a forward intake portion and a rearward, restricted discharge portion for discharging rearwardly of the stern of the craft; said forward intake portion has an inlet side and a discharge side, said inlet side being of smaller cross sectional area than said discharge side; a first stage, axial flow pump in said housing; a second stage, mixed flow pump in said housing and located reauwardly of said first stage pump for receiving Water therefrom; said housing being of substantially cylindrical shape from the inlet side of said first stage pump to the inlet side of said second stage pump, and the said housing then diverges rearwardly from the inlet side of said second stage pump to the discharge side of said second stage pump and then said housing converges rearwardly at its discharge portion; straightening vanes located rearwardly of each of said first and second stage pumps; and means for rotationally driving said pumps and said second stage pump faster than said first stage pump, said means for rotationally driving said pumips includes an engine and 6 gear reduction unit, said pumps being in co-axial alignment and driven by a sleeve and a shaft, said sleeve and shaft each being connected to said gear reduction unit for being rotationally driven.

References Cited UNITED STATES PATENTS 1,402,059 1/ 1922 Eich 103-94 3,082,732 3/ 1963 Stallman 103-93 XR 10 3,233,573 2/1966 Hamilton 115-16 3,269,111 8/ 1966 Brill 60-221 CARLTON R. CROYLE, Primary Examiner. 

